I have been meaning to ask this question for some time .... I think this has only happened since moving to V13. When editing a track segment that has a mitred segment attached to it, before V13, as you moved the track segment such that the mitre was becoming less and less, (till finally there is one straight track) ... if you kept moving, the mitre would re-appear again as a normal mitre. However in V13 when the mitre re-appears it shoots off in the opposite direction sometimes into a huge long track segment that then needs to be re-edited.
I haven't been able to reproduce this. Are you aware of the settings that you get during dragging?
If you right click without releasing the left button, you get options like 'Preserve attached segments' which are persistent. I'm wondering if one of these has been accidentally set and is causing the odd behaviour.
Preserve segments was ticked .... un-ticked it and back to normal operation.
I use a "vertical mouse" to relieve RSI .... on this type of mouse you cannot click both right and left at the same time so had to resort to a normal mouse to do this.